Abstract: We apply the recently defined multipole vector framework to the
frequency-specific first-year WMAP sky maps, estimating the low-l multipole
coefficients from the high-latitude sky by means of a power equalization
filter. While most previous analyses of this type have considered only heavily
processed (and foreground-contaminated) full-sky maps, the present approach
allows for greater control of residual foregrounds, and therefore potentially
also for cosmologically important conclusions. The low-l spherical harmonics
coefficients and corresponding multipole vectors are tabulated for easy
reference.
Using this formalism, we re-assess a set of earlier claims of both
cosmological and non-cosmological low-l correlations based on multipole
vectors. First, we show that the apparent l=3 and 8 correlation claimed by Copi
et al. (2004) is present only in the heavily processed map produced by Tegmark
et al. (2003), and must therefore be considered an artifact of that map.
Second, the well-known quadrupole-octopole correlation is confirmed at the 99%
significance level, and shown to be robust with respect to frequency and sky
cut. Previous claims are thus supported by our analysis. Finally, the low-l
alignment with respect to the ecliptic claimed by Schwarz et al. (2004) is
nominally confirmed in this analysis, but also shown to be very dependent on
severe a-posteriori choices. Indeed, we show that given the peculiar
quadrupole-octopole arrangement, finding such a strong alignment with the
ecliptic is not unusual.